CA1056972A

CA1056972A - Rubber composition

Info

Publication number: CA1056972A
Application number: CA250,408A
Authority: CA
Inventors: Yuichi Sugiyama; Hiroyuki Kaido; Tsuneo Koyama
Original assignee: Yokohama Rubber Co Ltd
Current assignee: Yokohama Rubber Co Ltd
Priority date: 1975-05-22
Filing date: 1976-04-15
Publication date: 1979-06-19
Also published as: FR2311797B1; JPS5720330B2; NL7603561A; DE2616613A1; US4082909A; FR2311797A1; DE2616613C2; JPS51136734A

Abstract

ABSTRACT OF THE DISCLOSURE
A rubber composition which is highly adherent to metallic materials by vulcanization comprises 0.5 -20 parts by weight of a metal salt of hydroxybenzoic acid per 100 parts by weight of a rubber. The adhesiveness of the composition to metallic materials is not much reduced by hot ageing.

Description

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The present invention relates to a rubber composition which is hightly adherent to metallic materials by vulcanization.
It is known to plate a steel product, e.g. a steel cord, with a copper alloy such as brass or bronze when the steel product and a rubber are to be adhered together. However, the demand for high speed, high load and high efficiency of motor car tires, conveyor belts, driving belts, V-belts and hoses, in which metallic materials are used as tension members, has increased. Accordingly, high adhesion between the rubber and the metallic material has been needed. Recently, in order to improve adhesion between the rubber and the metallic material, it has been proposed to add a mixture of a formaldehyde donor, a formaldehyde acceptor and a finely dispersed silica filler to the rubber. This mixture is known as the "HRH" system.
The "HRH" system may consist of, for example, fine silica, resorcinol and hexamethylenetetramine.
Rubber compositions incorporating the HRH system have the disadvantages that they generate smog and bad smells thereby polluting the environment and the workability of the composition in blending by a Banbury mixer or a roller mixer is reduced because of excessive sublimation of the resorcinol.
The rubber compositions also have the disadvantages that rolling workability is reduced because of low scorch safety and adhesive-ness is reduced because of moisture absorption in the unvulcan-ized condition.
It has been proposed to add cobalt naphthenate to a rubber in order to improve adhesiveness between the rubber and a metallic material. However, the addition of cobalt naphthenate causes the disadvantages that adhesiveness is reduced in high temperature blending operation or high temperature vulcanization (such as at 150 - 190C in the preparation) and adhesiveness is reduced and other physical properties are also adversely lOS6~7Z
affected after heat ageing; (such as at about 100C for several tens of hours in the driving).
It has now been found that the adhesion between a rubber and a metallic material can be markedly improved by adding a metal salt of hydroxybenzoic acid to the rubber.
Accordingly the present invention provides a rubber composition for bonding to a metallic material by vulcanization, r;
which composition comprises 0.5 - 20 parts by weight of a metal salt of hydroxybenzoic acid per 100 parts by weight of a rubber.
The present invention, at least in its preferred t embodiments and as compared with the prior art discussed above, enables adhesion between a rubber and a metallic material to be improved, enables the deterioration of adhesiveness due to heat ageing to be reduced, and improves the workability of the rubber in the preparation of products such as tires, belts and hoses. t-Suitable metal salts of hydroxybenzoic acid for use in the invention include anhydrous and hydrated hydroxybenZOic acid salts of Na, K, Mg, Ca, AQ, Fe, Sn, Ni, Co, Zn and Cu.
The metal salt of hydroxybenzoic acid is present in the rubber composition in an amount of 0.05 - 20 parts by weight per 100 parts by weight of the rubber.
In this specification, we use the abbreviation "wt. phr." which, in relation to an ingredient of the rubber composition, refers to parts by weight of the ingredient per 100 parts by weight of the rubber. If the rubber composition according to the invention were to comprise less than 0.5 wt.
phr. of the metal salt of hydroxybenzoic acid, the desirable '-effects of the invention would not be attained.
If the rubber composition of the invention were to comprise more than 20 wt. phr of the metal salt of hydroxybenzoic ' acid, delay of vulcanization and deterioration of physical ~OS~7~

properties would be caused.
The optimum amount of the metal salt of hydroxybenzoic acid in a composition according to the invention is dependent upon the type of the rubber in the composition, any additives present in the composition and the metallic material to which the composition is to be adheredand is usually in the range of 0.5 - 7 wt. phr. in order to give good adhesion of the composition to the metallic material.
Rubber compositlons according to the invention have excellent adhesion to iron, copper, brass, zinc, bronze and t aluminum. Rubbers which may be present in the rubber composition of the invention include diene rubbers such as natural rubber polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer, acrylonitrile-butadiene rubber and chloroprene rubber and mixtures thereof.
Rubber compositions according to the invention may t comprise vulcanizing agents including sulfur-vulcanization acceler- ' ator vulcanizing agents and peroxide vulcanizing agents. The ~ -vulcanization accelerator can be selected from a wide range of 20 compounds such as sulfenamides e.g. N-oxydiethylene benzothiazole , sulfenamide, thiazoles e.g. 2-mercapto-benzothiazole and thiurams e.g. tetramethyl thiuramdisulfide. t Rubber compositlons according to the invention may comprise other additives such as zinc oxide, stearic acid, ?
carbon black and fine silica (white carbon), depending upon the intended uses of the compositions. The vulcanization temper-ature of a rubber composition according to the invention may be a conventional vulcanization temperature. The present inven-tion may be considered in accordance with prior art such as: ;
Encyclopedia of Polymer Science and Technology Vol. 12 Pages 161-353 on rubbers; ibid Vol. 14 Pages 42 - 64 on tires and tire cord; ibid Vol. 8 Pages 184-185 on tire cord dip; ibid Vol. 14 ~0~697;~

Pages 740 - 756 on Vulcanization; and Rubber Chemistry and Technology 46(4) Pages 981 - 998 on rubber-to-textile and rubber-to-steel cord adhesion.
The invention will be further illustrated by detail by the following examples.
[1] Example 1 - 14; Standard Example 1 and Comparative Examples 1 - 2 The compositions stated in Table 1 and Table 3 were blended as described below. Test results of the rubber compositions of Examples 1 - 14, Standard Example 1 and Compara-tive Examples 1 - 2 are given in Table 2 and Table 4.
Preparation and Vulcanization of Rubber Compositions The components of each master batch were blended by a Banbury mixer and a vulcanizing agent was blended with the master batch on a two roll mill to prepare each rubber composition.
Adhesive strength test 1) Adhesive strength to metal material r Brass plated steel cords were arranged mutually parallel and spaced apart by 12.5 mm. Each rubber composition was coated on opposite sides of the steel cords to form a fabricated product in which each cord was embedded to a depth of 2 inches. The fabricated product was vulcanized at 150C for 30 mins. Pull-out tests were carried out on the fabricated products in accord- t ance with ASTM D2229. The tests were conducted on (1) products which had been cooled to room temperature after vulcanization but not heat aged and (2) products which had been cooled to room temperature after vulcanization and subsequently heat aged at 100C for 72 hours in a gear oven.
As it is clear from Table 2 and Table 4, the physical properties of the vulcanized rubber compositions of the invention are similar to those of the vulcanized rubber composition contain-ing cobalt naphthenate. However, the adhesive strength to the 10S~97'~
brass plated steel cord and the retention coefficient of adhesive strength after hot ageing of the compositions of the invention are markedly improved ascompared with the composition containing cobalt naphtenate.

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[II] Examples 15-23: Standard Example 2 and Comparative Examples 3 - 5 In accordance with the process of [I], the compositions stated in Table 5 were blended, vulcanized and physical properties of the products were measured. The test results are shown in Table 6. As it is clear from the results of Table 6, the physical properties especially tensile strength under 300~ and elongation of the vulcanized rubber compositions of the invention were markedly improved compared with those of the vulcanized rubber composition containing cobalt naphthenate. The adhesive strengths to zinc plated steel cord and non-plated steel cord of the vulcanized rubber compositions of the invention were markedly improved by the addition of the metal salts of hydroxybenzoic acid especially the cobalt salt of p-hydroxybenzoic acid. The retention coefficient of adhesive strength after heat ageing were also markedly improved.

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As stated above, the rubber compositions of the invention j enable a remarkably high adhesive strength to metallic material to be attained and prevent deterioration of adhesiveness caused by heat ageing. The rubber compositions of the invention can be blended at high temperature (hot blending) and vulcanized , at high temperature (hot curing) to improve the processability of ~-the compositions as compared with the rubber compositions contain-ing cobalt naphthenate. Accordingly, the rubber compositions of the invention can be utilized as adhesive compositionsfor rubber which is to be bonded to a metallic material. ~ ' ~:.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A rubber composition for bonding to a metallic material by vulcanization, which composition comprises 0.5 - 20 parts by weight of a metal salt of hydroxybenzoic acid per 100 parts by weight of a rubber.

2. A rubber composition according to Claim 1, wherein said rubber is natural rubber or a vulcanizable synthetic rubber.

3. A rubber composition according to Claim 1, wherein the composition comprises a sulfur-vulcanization accelerator vulcanizing agent or a peroxide vulcanizing agent.

4. A rubber composition according to Claim 1, wherein said metal salt of hydroxybenzoic acid is selected from Na, K, Mg, Ca, A?, Fe, Sn, Ni, Co, Zn and Cu salts of hydroxybenzoic acid.

5. A rubber composition according to Claim 1, wherein said metal salt of hydroxybenzoic acid is cobalt hydroxybenzoate.

6. A rubber composition according to Claim 1, wherein said metal salt of hydroxybenzoic acid is nickel hydroxybenzoate.

7. A vulcanized rubber product reinforced with metallic cords, which product comprises a rubber composition comprising 0.5 - 20 parts by weight of a metal salt of hydroxybenzoic acid per 100 parts by weight of a rubber.

8. A vulcanized rubber product according to Claim 7, wherein said metallic cords are copper alloy coated steel tire cords.

9. A vulcanized rubber product according to Claim 7, wherein said metal salt of hydroxybenzoic acid is selected from Na, K, Mg, Ca, A?, Fe, Sn, Ni, Co, Zn and Cu salts of hydroxybenzoic acid.

10. A vulcanized rubber product according to Claim 7, wherein said metal salt of hydroxybenzoic acid is cobalt hydroxy-benzoate.

11. A vulcanized rubber product according to Claim 7 wherein said metal salt of hydroxybenzoic acid is nickel hydroxybenzoate.